Electronic printing includes all ink jet printing, such as continuous ink jet printing, and all other systems wherein images are dried to fix the image on the substrate, as well as ionography, electrophotography, and all other systems wherein toner is fused to fix the image on the substrate. Current electronic printing presses are configured with a standard fuser/fixer or fixer/dryer system and are capable of drying at high speed, and full width.
Conventional printing presses arrange all the apparatus for printing in a tower. Paper is fed to the tower by appropriate paper feeding apparatus using either sheets of paper, or a continuous web of paper. Typical color printing presses utilize multiple "towers". The paper is fed sequentially from one tower to the next, each tower printing a particular color (or sometimes a transparent coating). For printing processes which require fixing of one color ink before the next color ink is printed, a standard fixer/dryer is used between towers.
When it is desired to print on both sides of a substrate, there are several options in common usage. In one common web press configuration the first side is printed in a first tower and then a second tower is used for printing on the reverse side. In this type configuration, a turnbar is required between towers. A turnbar is an arrangement of rollers which have the effect of inverting the web so that the unprinted side of the paper is available for printing in a subsequent tower. Typically, at least four colors are needed on each side of the paper, so eight towers are required. Obviously, the result is a long printing press, especially if dryers are required between print impressions. Long printing presses have associated problems which include excessive floor space requirements and, for digital printing systems, excessive data memory requirements.
Furthermore, when printing at high speeds with ink jet presses, a roller is needed on the unprinted side of the substrate to hold the web flat and close to the printhead, and the "wet" side of the substrate cannot be contacted immediately after printing.
Current designs to position the substrate under the printheads for imaging are often too big for some applications, and limited in application. Prior art designs were intended to serve traditional markets where floor space for the imager was not a primary concern. Duplex and second pass imaging was performed simply by adding another tower down stream of the first tower. This tandem arrangement could then image duplex documents or multiple colors with variable information.
It is seen, then, that there is a need for an improved electronic printing architecture whereby a webbed substrate could be fed into a single system tower when space consideration is a constraint, yet still provide duplex documents and printed images with multiple colors.